What is it like to be a serpent?
30 July 2013
One of the most famous thought experiments of twentieth century philosophy of mind is presented in Thomas Nagel’s paper “What is is like to be a bat?” Nagel’s point was that consciousness involves a point of view, and that means that there is something that it is like to be in being some conscious organism. Here is the opening paragraph of Nagel’s paper:
Conscious experience is a widespread phenomenon. It occurs at many levels of animal life, though we cannot be sure of its presence in the simpler organisms, and it is very difficult to say in general what provides evidence of it. (Some extremists have been prepared to deny it even of mammals other than man.) No doubt it occurs in countless forms totally unimaginable to us, on other planets in other solar systems throughout the universe. But no matter how the form may vary, the fact that an organism has conscious experience at all means, basically, that there is something it is like to be that organism. There may be further implications about the form of the experience; there may even (though I doubt it) be implications about the behavior of the organism. But fundamentally an organism has conscious mental states if and only if there is something that it is to be that organism—something it is like for the organism.
The choice of a bat for this thought experiment is interesting. As a mammal, the bat shares much with us in its relation to the world, but its fundamental mechanism of finding its way around — echolocation — is sharply distinct from our primate experience of the world, dominated as it is by vision. Thus while what it is like to be a bat overlaps considerably with what it is like to be a hominid, there are also substantial divergences between being a bat and being a hominid. A bat has a different sensory apparatus than a hominid, and the bat’s distinctive sonar sensory apparatus presumably shapes its cognitive architecture in distinctive ways.
As a philosopher I have a great fascination with the sensory organs of other species, which seem to me both to pose epistemological problems as well as to suggest really interesting thought experiments. In my post on Kantian Critters I argued that if human beings must have recourse to the transcendental aesthetic in order to sort out the barrage of sense perception that the brain and central nervous system receive, then other terrestrial species, constituted as they are much like ourselves, must also have recourse to some transcendental aesthetic of their own (or, if you prefer Husserl to Kant, and phenomenology to idealism, other species must employ their own passive synthesis). This interpretation of Kant obviously presupposes a naturalistic point of view, which Kant did not have, but if we grant this scientific realism, the Kantian insight regarding the transcendental aesthetic remains valid and may moreover be extrapolated beyond human beings.
Distinctive transcendental aesthetics of distinct species would follow from distinct sensory apparatus and the distinctive cognitive architecture required to take advantage of this sensory apparatus. This implies that distinct species “see” the world differently, with “see” here understood in a comprehensive sense and not in a purely visual sense. Although bats rely on sonar, they “see” the world in his comprehensive sense, even if their eyes are not as good as our hominid eyes, and not nearly as good as the eyes of an eagle. A couple of ethologists, Dorothy L. Cheney and Robert M. Seyfarth, have written several books on the Weltanschauung of other species, How Monkeys See the World: Inside the Mind of Another Species and Baboon Metaphysics: The Evolution of a Social Mind.
Does a primate have more in common, Weltanschauung-wise (if you know what I mean), with a flying mammal such as a bat (since any two mammals have much life experience in common) or with a terrestrial reptile such as a serpent? Primates don’t know what it is like to fly with their own wings, but they also don’t know what it is like to move along the ground by slithering. Does a primate have more in common, again, Weltanschauung-wise, with a reptile that has given up its legs or with an octopus that never had any legs? We might be able to refine these questions a bit more by a more careful consideration of particular sensory organs and the particular cognitive architecture that both is driven by the development of the organ and makes the fullest exploitation of that organ for survival and reproductive advantage possible.
Among the most intriguing sense organs possessed by other species but not by homo sapiens is the pit of the pit viper, which is a rudimentary sensing organ for heat. Since pit vipers are predators who typically eat small, furry animals with a high metabolism and presumably also a high body temperature, being able to sense the body heat of one’s prey would be a substantial selective advantage.
Because the pit of the pit viper represents such a great selective advantage, one would expect that the pit will evolve, driven by this selective pressure. To paraphrase what Richard Dawkins said of wings, one percent of a infrared sensing organ represents a one percent selective advantage, and so on. Thus a one percent improvement of an existing pit would represent another one percent selective advantage. While it would be difficult to observe such subtle advantage in the lives of individual organisms, when in comes to species whose members number in the millions, that one percent will eventually make a significant difference in differential survival and reproduction. A statistical study would reveal what a study of individuals would likely obscure.
There is a sense in which the pit of the pit viper is like an eye for perceiving infrared radiation. The infrared radiation spectrum lies just beyond the visible spectrum at the red end, so having a pit like a pit viper in addition to color vision would be like being able to see additional colors beyond red. Having a slightly different visible spectrum is not uncommon among other species. Many insects see a little way into the ultraviolet spectrum (at the opposite end of our visible spectrum from red) and flowers are said to present colorful displays to insects in the ultraviolet spectrum that we cannot see (except for the case I heard about some years ago about a man whose eye was injured and as a result of the injury was able to see a little way into the ultraviolet beyond the visible spectrum).
The eye itself, whatever portion of the electromagnetic spectrum it accesses, is a wonderful example of the power of an adaptation. The eye is so useful that it has emerged independently several times in the course of evolution of life on earth. I don’t know much about the details, but insect eyes, mollusc eyes, and vertebrate eyes (as well as several other instances) are each the result of separate and independent emergence of the eye. The mollusc eye and the vertebrate eye represent an astonishing example of convergent evolution, since the structure of the two instances of eyes is so similar. The eye is of course a provocative evolutionary example because of a famous passage from Darwin himself, who wrote about “organs of extreme perfection”:
“To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real. How a nerve comes to be sensitive to light, hardly concerns us more than how life itself first originated; but I may remark that several facts make me suspect that any sensitive nerve may be rendered sensitive to light, and likewise to those coarser vibrations of the air which produce sound.”
Of this quote Richard Dawkins wrote in The God Delusion:
“Darwin’s fulsomely free confession turned out to be a rhetorical device. He was drawing his opponents towards him so that his punch, when it came, struck the harder. The punch, of course, was Darwin’s effortless explanation of exactly how the eye evolved by gradual degrees. Darwin may not have used the phrase ‘irreducible complexity’, or ‘the smooth gradient up Mount Improbable’, but he clearly understood the principle of both.”
Partly due to this Darwin quote, the evolution of the eye has been the topic of some very interesting research that has helped the clarify the development of the eye. There is a wonderful documentary on evolution, the first episode of which was titled Darwin’s Dangerous Idea (presumably intended to echo Daniel Dennett’s well known book of the same title), which an excellent segment on the evolution of the eye which you can watch on Youtube. In this documentary the work of Dan-Eric Nilsson of the University of Lund is shown, and he demonstrates in a particularly clear and concrete way the step-by-step process of improving vision through the increasing complexity of the eye. When I was watching this documentary recently I was thinking about how the pit of the pit viper resembles the early stages of the evolution of the eye.
The pit of the pit viper is a depressed, folded area lined with infrared sensitive nerve endings that allows limited directional sensitivity. In the long term future of the pit of the pit viper, which at present seems to correspond to the earliest stages of the evolution of the vertebrate eye, sometimes called a “cup eye,” there would seem to be much room for improvement. Of course, the details of infrared (IR) perception are different than the details of human visible spectrum perception, but not so different that we cannot imagine a similar series of stepwise improvements to the infrared pit that might, in many millions of years, yield sharp, clear, and directional infrared vision. If this infrared vision became sufficiently effective, it is possible that brain and body resources might be redirected to focus on the pits, and the eyes could eventually degrade into a vestigial organ, as in bats and moles. After all, snakes gave up their legs, so there’s no reason they shouldn’t also give up their eyes if they have something better to fall back on.
There is another possibility, and that is the evolutionary advantage that might be obtained through adding a pair of fully functional IR “eyes” to a pair of fully functional visible spectrum eyes. Such a development would be biologically costly, and it would be much more likely that a pit viper would chose one evolutionary path or the other and not both. Yet there are some rare instances of biologically costly organs (or clusters of organs) that have been successful despite the cost. The brain is a good example — or, rather, large complex brains that evolve under particular selection pressures but which later are exapted for intelligence.
Natural selection is a great economist, and often reduces organisms to the simplest structure compatible with their function. This is one of the reasons we find the shapes of plants and the bodies of animals both elegant and beautiful. The economy of nature was resulted in the fact that a large brain, and the intelligence that large brains make possible, are rare. Despite their rarity, and their biological expense, large complex brains do emerge (though not often), and, like the eye (which has emerged repeatedly in evolutionary history), large brains have emerged more than once. Interestingly enough, complex eyes and large complex brains are found together not only in primates but also in molluscs.
The octopus (among other molluscs) is bequeathed a large, complex brain because the octopus went down the evolutionary path of camouflage, and the camouflage of some molluscs became so elaborate that almost every cell on the surface of the organism’s skin is individually controlled, which means a nerve connected to every spot of color on (or under) the skin, and a nervous system that is capable of handling this. It requires a lot of processing power to put on the kind of displays seen on the skin of octopi and cuttlefish, and an evolutionary spiral that favored the benefits of camouflage also then drove the development of a large, complex brain that could optimize the use of camouflage.
The octopus also has remarkably sophisticated eyes — eyes that are, in some respects, very similar to yet more elegant in structure than primate eyes. Our eyes are “wired” from the front, which gives us a blind spot where the optic nerve passes through the retina; mollusc eyes are “wired” from the back and consequently suffer from no blind spot. (“Wired” is in scare quotes here because it is a metaphor to refer to eyes being wired to the nervous system; while electrical signals travel down nerves, the connection between distinct nerve cells is primarily biochemical and not electrical.)
How an octopus sees the world is as fascinating an inquiry as what it is like to be a bat — or a serpent, for that matter. Both the octopus and an arboreal primate live in a three dimensional habitat, and this may have something to do with their common development of sharp eyesight and large brains, although there are vastly greater number of organisms in the sea and in trees with far smaller brains and far less cognitive processing power. (A recent study reported in The New York Times suggests a link between spatial ability and intellectual innovation, and while the study was primarily concerned with the ontogenesis of creativity, it is possible that the apparatus of spatial perception and the cognitive architecture that facilitates this perception is phylogenetically linked to intellectual creativity.) This simply shows us that intelligence is one strategy among many for survival, and not the most common strategy.
A large, complex brain is very costly in a biological sense. In a typical human being, the brain represents less than three percent of total body weight, yet it consumes about twenty percent of the body’s resources — that’s a very big chunk of metabolism that could be directed toward running faster or jumping higher or reaching farther. Nothing as unlikely as the brain’s disproportionate consumption of resources would come about unless this expenditure of resources bequeathed some survival or reproductive advantage to the organism possessing such a high cost of ownership. The brain isn’t a luxury that produces poetry and art; it is a survival machine, optimized (in hominids) by more than five million years of development to make human beings effective hunters and foragers. The brain was so successful, in fact, that it made is possible for human beings to take over the planet entire and convert it to serving human needs. Thus the relatively rare and costly strategy of developing a large, complex brain paid off in this particular case. (One may think of it as a high risk/high reward strategy.)
If the evolution of the brain and the exaptation of intelligence to produce civilization did not result in the disproportionate evolutionary success of a single species, it seems likely that we would see intelligence emerge repeatedly in evolutionary history, much as eyes have evolved repeatedly. On other worlds with other natural histories, under conditions where intelligence does not allow a single species to dominate (possibly due to some selection pressure that does not operate on Earth), it is possible that evolution results in the repeated emergence of intelligence just as on Earth evolution has resulted in the repeated emergence of eyes. On Earth, intelligence preempted another developments, and means that not only human history but also natural history were irremediably changed.
In The Preemption Hypothesis I argued that industrialization preempted other developments in the history of civilization (for more on this also see my post Human Agency and the Exaptation of Selection). This current line of thought makes me realize that purely biological preemption is also a force shaping history. Consciousness, and then intelligence arising from biochemically based consciousness, is one such preemption of our evolutionary history. Another preemption of natural history that has operated repeatedly is that of mass extinction. But whereas historical preemptions such as the development of large, complex brains or industrialization represent a preemption of greater complexity, mass extinctions represent a preemption of decreased complexity.
It seems that “weedy” species that are especially hearty and resilient tend to survive the rigorous of mass extinctions; the more delicate and refined productions of natural selection, which are dependent upon mature ecosystems and their many specialized niches, do not fare as well when these mature ecosystems are subject to pressure and possible catastrophic failure. One could think of mass extinctions, and indeed of all historical preemptions that favor simplicity over complexity, as a catastrophic “reset” of the evolutionary process. Events such as mass extinctions can favor rudimentary organisms that are sufficiently hardy to survive catastrophic changes, but, as we have seen, there is also the possibility of historical preemptions that favor greater complexity. The Cambrian Explosion, for example, might be considered another instance of an historical preemption.
There is a tension in the structure of history between continuity and preemption. In the particular case of the earth, the continuity of natural history has been interrupted by the preemption of intelligence and then industrialization. These preemptions of greater complexity — in contradistinction to preemptions of lesser complexity, as in the case of mass extinctions — may provide for the possibility of the continuity of earth-originating life beyond the terrestrial biosphere. In the case of an otherwise sterile universe, the intelligence/industrialization preemption would be a basis of a new explosion or radiation of earth-originating life in the Milky Way. In the case of a universe already living, it may be only intelligence and industrial-technological civilization that is a novelty in the natural history of the universe.
Whatever happens on the largest scale of life, as long as life continues to evolve on the earth, its development is likely to be marked by both continuity and preemptive developments. In thinking about the pit viper, I suggested above that the pit viper might eventually, over many millions of years, develop a fully functional pair of IR eyes in addition to its visible spectrum eyes. This suggestion points to an interesting possibility. In so far as complex life is allowed to develop in continuity, with a minimum of preemptions, specialization and refinement of existing mechanisms of survival may give rise of species of greater complexity than what we know today. While mass extinctions have repeatedly cleared the ground and given a more or less blank slate for the radiation of resilient weedy species, this may not always be the case.
As our earth and the solar system of which it is a part becomes older, catastrophic events may become less common. For example, stray bodies in the solar system that might collide with the earth, while once common in the early solar system, eventually end up colliding with something or getting swept out of the path of the earth’s orbit by the gravity of Jupiter. If, moreover, civilization expands extraterrestrially and seeks to protect the earth as an existential risk mitigation measure, life on earth may become even more secure and even less subject to disruption and preemption than in the past. New species might eventually come into being with a delicate complexity of sensory organs and accompanying cognitive architecture that facilitates these senses. Imagine species with a whole range of sensory organs that complement each other, without former mainstay sensory organs being reduced to vestigial status, and this might possibly be the future of life on Earth.
Eventually the most interesting question may not be, “What is it like to be a serpent?” but, “What will it be like to be a serpent?”
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The reader can compare my earlier post, The Future of the Pit Viper, which was the origin and inspiration of this post.
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